A former top aide to Gov. Andrew M. Cuomo was found guilty on Tuesday of three corruption-related charges, a repudiation of the murky back-room dealings in Albany laid bare during the nearly eight-week trial.

The conviction capped a stunning fall for the former aide, Joseph Percoco, once the governor’s executive deputy secretary and longtime confidant. He was convicted of soliciting and accepting more than $300,000 in bribes from executives working for two companies with state business.

And even though Mr. Cuomo, a Democrat, was not accused of wrongdoing, the verdict still underscored ethical lapses and illegal activity at a time when Mr. Cuomo is seeking re-election.

In a statement several hours after the verdict, the governor said that while he was saddened for Mr. Percoco’s young daughters, he believed there should be “no tolerance” for lapses of integrity in public service.

“The verdict demonstrated that these ideals have been violated by someone I knew for a long time. That is personally painful,” the governor said. “However, we must learn from what happened and put additional safeguards in place to secure the public trust. Anything less is unacceptable.”

At the height of his influence, Mr. Percoco, whom Mr. Cuomo had once described as his father’s “third son,” was known as the governor’s enforcer, responsible for everything from keeping lawmakers in line and intimidating Mr. Cuomo’s political rivals to making sure chairs and thermostats were in order for the governor’s public appearances.

After eight days of strained deliberations, the jury in Federal District Court in Manhattan delivered a split verdict: It found Mr. Percoco not guilty of extortion and conspiracy to commit extortion, but appeared to find fault with his dealings on behalf of Competitive Power Ventures, a Maryland-based power company.

The trial painted an unflattering portrait of Mr. Percoco and more broadly of the inner workings of the state capital, one replete with expensive fishing trips, clubby nicknames and “magic phone calls” that could make or break multimillion-dollar contracts.

Of the more than $300,000 in alleged bribes to Mr. Percoco, prosecutors said the bulk came from Competitive Power Ventures, in the form of a “low-show job” for Mr. Percoco’s wife, Lisa Toscano-Percoco.

Ms. Toscano-Percoco was paid a yearly salary of $90,000, for a total of about $285,000, to teach schoolchildren about energy. She was given the job by a CPV executive, Peter Galbraith Kelly Jr., one of Mr. Percoco’s co-defendants in the trial.

The jury found Mr. Percoco guilty of two criminal counts — one of conspiracy to commit honest services fraud and one of soliciting bribes — related to the alleged CPV scheme, but could not reach consensus on Mr. Kelly’s involvement.

Mr. Percoco was also found guilty of one count of conspiracy related to a separate Syracuse-area development company, as was a co-defendant, Steven Aiello, an executive with that company; a fourth defendant, Joseph Gerardi, also of the development company, was acquitted of all charges.

Mr. Percoco told reporters after the verdict that he was disappointed and that he and his lawyers would review options for appeal.

“I’m thankful to my family and friends that have stood by me through this entire process,” he said, “and I look forward to them all standing by me as we go forward.”

Milton L. Williams Jr., a lawyer for Mr. Gerardi, said he was “very relieved, obviously, for him and his family.”“Obviously, I feel very bad for Mr. Aiello and Mr. Percoco,” he added.

The jurors made clear virtually from the start that they were struggling to reach consensus. Last week, after less than 20 hours of deliberations, they declared themselves deadlocked; sent back by the judge to continue deliberating, they declared themselves deadlocked again on Monday.

The panel’s mounting frustration was evident, especially as the trial dragged well beyond its projected four- to six-week finish. Several jurors asked to be dismissed from the case, citing its physical and emotional toll.

After the trial, jurors declined to comment — except one who, as she strode away from the courthouse, offered that she was “happy it’s over.”

The United States attorney in Manhattan, Geoffrey S. Berman, said in a statement that Mr. Percoco had sold “something priceless that was not his to sell: the sacred obligation to honestly and faithfully serve the citizens of New York.”

Much of the government’s narrative of the bribery schemes revolved around Todd R. Howe, a disgraced former lobbyist and longtime Albany insider, who prosecutors said engineered the bribes from the executives to Mr. Percoco.

Mr. Howe, who had pleaded guilty to eight felonies and was cooperating with prosecutors, described how Mr. Percoco helped COR Development, the Syracuse company that employed Mr. Aiello and Mr. Gerardi, evade a costly union requirement on a development, and wangled a pay raise for Mr. Aiello’s son, who worked in state government. In return, Mr. Howe said, Mr. Percoco pressured the executives to help his wife land the job with the power company or to funnel thousands of dollars a month in covert payments.

But Mr. Howe at times seemed poised to be the prosecution’s downfall, rather than its linchpin.

In early February, he was arrested midway through his testimony, after admitting during cross-examination that he had attempted to defraud his credit card company — after signing his cooperation agreement with the government.

The shocking development bolstered defense arguments that Mr. Howe was a self-interested liar whose testimony could not be believed; lawyers monitoring the case called the arrest a prosecutor’s worst nightmare.

Prosecutors also suggested that Mr. Percoco had violated New York State election and ethics laws by continuing to intervene in state business even after he left to work in the private sector. Witnesses said they had often seen Mr. Percoco in Mr. Cuomo’s New York and Albany offices even after he was no longer a state employee. Public records indicate that Mr. Cuomo was often in the office at the same time.

And if the dealings themselves were not unseemly enough, prosecutors said, many were carried out via bullying, name-calling and thinly veiled code words; Mr. Percoco’s and Mr. Howe’s use of “ziti” to refer to money — a nod to the Mafia drama “The Sopranos” — was a frequent motif.

Advocates for government reform called the trial’s outcome an indictment of Albany’s culture. Blair Horner, the executive director of the New York Public Interest Research Group, said he hoped the verdict would compel Albany “to deal with its ethics problem.” John Kaehny, executive director of Reinvent Albany, said the trial had revealed a state government “riddled with pay-to-play influence-peddling.”

“The governor has to redeem himself,” Mr. Kaehny said.

Other major Albany corruption trials are scheduled to follow in the coming months: those of Sheldon Silver, a Democrat and longtime former Assembly speaker, and Dean G. Skelos, a Republican and former Senate majority leader. Both men are being retried after their convictions were overturned on appeal last year.

And in June, another former Cuomo ally, Alain E. Kaloyeros, will stand trial in a case that may cast further unflattering light on the governor’s administration. The trial of Mr. Kaloyeros, the former president of the State University’s Polytechnic Institute, involves bid-rigging in Mr. Cuomo’s signature upstate economic development plan, the so-called Buffalo Billion. Mr. Aiello and Mr. Gerardi also face charges in that trial.

Mr. Howe was expected to testify in the Buffalo trial as well.

Barry A. Bohrer, a lawyer for Mr. Percoco, declined to address a question about whether Mr. Percoco, who is scheduled to be sentenced by Judge Valerie E. Caproni on June 11, was a victim of political maneuvering. But, he said, “it is a difficult time and place to be trying a case involving Albany politics.”

Asked outside the courthouse if he had spoken to Mr. Cuomo about the verdict, Mr. Percoco cracked a smile.